Because of the increasing use of total joint replacements and the need to correctly diagnose mechanical degradation of such implants a technique of in vivo joint monitoring by means of acoustic emission will be developed. In order to accomplish this the acoustic emission signatures of implant metals, polymethylmethacrylate and bone will be developed under appropriate loading conditions. Composite in vitro structures consisting of cadaver bone, polymethylmethacrylate and appropriate implanted total joint replacements will then be monitored for their acoustic emissions while subjected to heavy static and cyclic loads. A two microphone technique will be utilized so that the locations of the emission sources may be detected in two-dimensional space. A finite element analysis will be provided utilizing appropriate material properties and geometries so that correlations between predicted high stress areas and regions of acoustic emissions may be performed. When sufficient accuracy and repeatability has been achieved in the in vitro studies an in vivo program will be initiated using the identical available equipment. The patient population from the Hip Service of the Hospital for Special Surgery will provide the patient volunteers. Those patients who have a high risk factor based on clinical variables such as weight, bone size and level of activity will be monitored and correlations between continued clinical findings and acoustic emission findings will be performed.